Method of making phosphor screens



June 17, 1952 J. E. RUEDY ET Al.

METHOD oF MAKING PHosPHoR SCREENS Filed June 5, 1946 Flai Patented June 17, 1952 UNI TED S APA.:"lENl v2,6110579 MirrironVV or MAKING PHosPHoR` scnE'ENs John needy and Fera E.fvv'il1iams,flrinfcftn,

NJ .,la's'signrsjto- Radio/'Corporation 'of-Amer'- ica', a corporation cof Delaware Application Janes, 1946', Seriai No. 674,587

roei-nhs. (Griff-'43am This invention relates to the inakihgof'phosphors for production of fluorescent light.

Phosphors,k asv a general rule, have been made by heating the proper mixture of compounds, in cluding theV activators, inv a furnace and then cooling and grinding to the'desired state'of neness for application to the phosphor base.

It has heretofore been found that-,1a phosphor may be made by simultaneously evaporati'ng fzinc fluoride and n ianganese activator in the same Crucible and condensing their vapors on' asuitab1e body. This is satisfactory for Azinc' fiuoride Yand manganese activator, as they have about the same volatility and the methodv providesmgood activation.y Wehave, however, since foundthat, i101, man3?V Phosphor mfafls. eihell'llth 0r with' out foreign activators, this method will not produce asuitable phosphoneither because they have too great a difference 'in Volatility or a separate niethodof activation is required.

It is an object of ouninvention to provide a methodnof making a highly efficient phosphor oi a material or materials, with or withoutforeign activators, some or all of which have Widely differentvolatility.

It is a furtherobject of our invention to provide amethod of making a phosphor of sulphides'and sulphoselenides of cadmium and Zinc with or Without silver or copper activators.A

Other objectsof our invention will appear in the following description, reference beingr had to the drawing, in which;

Fig. 1 isa section through the evaporating and condensing apparatus for carryingout-'our `invention.

Fig.-2 isa section through aflurnacefor activation of theph'osphor.

Our invention'may be used with various-phosphor materials, but we have found itpparticu-larly satisfactory for zinc; and cadmium sulphide and zinc sulphoselenide; 'either with or without foreign activators such as silver or copper. In carrying out our process, a Pyrex glass disc I constituting the base forthe phosphor isplacedona suitable stand' 2' in the vacuum chambenfeomprising a bell 3 resting on a base 4 with "gasfls'etY 5tomake an airtight joint.l vAdjacent-the' disci, say beneath it, are placed as many cruciblesA as are needed. for carrying out the process. We have shown three of these, namely 6, 'I and 8, which may be platinum tubes with` closed bottoms" and open tops, containing the materials to be evaporated. For heating these crucibles it is convenient to connect one terminal" 9"of the heating systemf to one end of the tube crucibles andflea'ds I ULi I I" and -I 2 fromtheiothef'terninal arefcon- 2 o nectedi to the opposite end of the 'tube'. These leads'may include rheostats I4; I5 and` i6' and amineters I'I, I8V and I9,'s'o `that proper"'current may be 'sent through thethin tubes to heatth'em to the desired temperature for valzo'rizirigl VV'the contents inside the tube. To produce zincL sulplioselenide a proper vacuum would be maintained by connecting the pipe 2Ilto' a suitablep'ump' and the rheostats would bef adjusted to v'ap'or'ze,"y say, zinc sulphide incrucible 6,`zinc selenid in-crucible If vand 'copper Sulphi'dein c'riicible 8.

The simultaneous depositions' of the 'various consttuents'are controlled in the following 'Inanner: A separate evaporation is' made from each crucible (6, 'I and 8) v up'on'P'yrex test' discs at ac'- curat'ely' known distances and heating currents for krvviilngtlfls Of time and. the iesulthg"de posits on the test discs vveighed'byy rn'eans'of a micro-balance, From `Athis, the rates of vaporation'of the constituents are determined',and the relative rates o f simultaneous deps'itiorfor'the final phosphor synthesis may be firclby adjustingfwith spacers 2I the distances',(accOrdinMthe inverse square law) of the different"cruciblef-G, 1v and" 8 fromthe P y'reii disc I andheatingf'aoh at its predetermined current.

I'he vapors from the three materials condense ontheunder sideV ofv thePyrex disc I Vand 4the proper thicknesscan be determined" by observingv the colored rings produced by light'iriterf'e'rcnce phenomena. It has heretofore been 4supposed thatheating the activatorfto its'vapoifaing tem,- perature and condensing' it With the "phosphor I nateria'lxvas suicientffor' activation purposes, butwe'ha've found'thatthis is not'the case'with these phosphore. To make-an eflicient phosphor out of theA condensed materials, itis necessary lto separately 'activate them. v

lTo accomplish the Iactivationof thev condensed materials, We take two discs that have been treated by the process above outlined and place them almost together, withthe'condensed materials on the inside. Wehave found-that" a suitableseparation is .the thickness ffthe usualfmicroscope cover' glass. Thesey tw'c'idiscs;- as 'thus assembled, are ,placed on suitable supports" 2-2: inside fany" desiredtype of furnacepsuchasa tube 523 having a heating coil i241 and ends 25,' 26. With theheat'- ing coil arranged with the? 'phosphor-'deposited layer' facingv each .other-in the way described, therev is no attempttov evacuate 'the' oven-fand atmospheric air may be left -therein.` Oneof-` the ends' may have a temperatura-indicating* device 21,- such as a therinocouple. 'The ovenislieatd "tot af' temperature of frriOO" "tof 650W oi'approximatelylone'hur. x I

f no copper or silver activator is to be used in the'phosphor and activation is solely to be produced by what free zinc is dissociated from the selenides or sulphides, then the zinc sulphide and zinc selenide alone will be heated to condense their vapors on the Pyrex disc I.

If a phosphor of zinc cadmium sulphide with a, say, silver activator is to be produced, the zinc sulphide would be placed in, say, crucible 6, cadmium sulphide in crucible 1 and a silver salt in crucible 8 at the proper relative distances and simultaneously heated at predetermined currents, as previously described. After these materials have been condensed on the discs, they are placed in the oven in the way already described and activated by heating to the temperature mentioned.

If zinc cadmium sulphide is to be used without a foreign activator, then no activator would be placed in a crucible, such as 8, and the zinc cadmium sulphide would be condensed on the disc, but nevertheless the zinc cadmium sulphide deposit on the Pyrex glass must be separately activated by heating to the temperature mentioned in a separate step.

We have found that; the atmosphere adjacent the condensed material on the Pyrex discs has a great deal to do with the production of an efiicient phosphor by the separate activation step. If the surface is activated in atmospheric air, an ine'lcient phosphor results. Ii, however, the oven shown in Fig. 2 is filled with nitrogen instead of air, a fairly efficient phosphor results. However, the most emcient phosphor that we have been able to produce is activated in substantially its own vapor. The placing of the two discs with the phosphor surface adjacent each other with a very thin spacing between them does not exclude the air in the sense that no air exists between the plates, but this space is so small that when heat is applied it is believed that suilicient vapor is produced adjacent the lm surface to remove the air from contact with the deposited film and a very efficient phosphor results by this form of activation. The phosphor during activation is essentially in an atmosphere of its own vapor.

By our process we produce directly on the target base to be incorporated in the cathode ray tube a very thin film that is uniform, non-grainy and homogeneous.

We have also produced Zinc sulphide phosphor, as well as zinc selenide phosphor by evaporating each of these salts and then separately activating them in the Way described, but the combination of the two makes the best phosphor. This may be due to some effect produced by the sulphoselenide, or it may be due to the mutual iiuxj ing action of the two salts in the activation process.

We claim:

1. The method of making a phosphor screen on a plurality of supports from a phosphor compound formed of a metal from the group consisting of zinc and cadmium and mixtures thereof and of a non-metal from the group consisting of sulfur and selenium and mixtures thereof, said method comprising the steps of, arranging said compound adjacent said supports within a vacuum, vaporizing said compound, condensing the vapors of said compound to form a coating of the condensate on a surface of said base members, placing two coated surfaces of said base members face to face and closely adjacent to each other, activating said condensate at atmospheric pressure by heating said base member to a temperature between 400 C` and 650 C., and separating said base members from each other to provide a support having an outer lm of activated phosphor material.

2. IThe method of making a phosphor screen from a phosphor compound formed of a metal from the group consisting of zinc and cadmium and mixtures thereof, and of a non-metal from the group consisting of sulfur and selenium and mixtures thereof, said method comprising the steps of, simultaneously vaporizing in a vacuum said compound and an activator, condensing the Vapor of said compound and activator to form a coating of the condensates on a surface of a plurality of base members, placing two coated surfaces of said base members face-to-face and closely adjacent to each other, activating said phosphor compound by heating said coated base members at atmospheric pressure to a temperature between 400 C. and 650 C., and separating said base members from each other to form a support having an outer film of activated phosphor material.

3. The method of making a phosphor screen on a plurality of support members from zinc sulphide and an activator, said method comprising steps of, arranging within a vacuum said Zinc sulphide and said activator adjacent said supports, vaporizing said zinc sulphide and said activator, condensing the vapors of said zinc sulphide and activator on at least one surface of each of said support members, placing two coated surfaces of said support members face to face and closely adjacent to each other, activating said zinc sulphide phosphor by heating said base members and said condensates to a temperature between lL00" C. and 650 C. and substantially solely in the vapors of said condensates thereof, and separating said support members from each other to provide supports each having an outer film of activated phosphor material.

4. The method of making a phosphor screen from zinc and cadmium sulphides and an activator, said method comprising the steps of, simultaneously vaporizing in a vacuum said zinc and cadmium sulphide and said activator, condensing the vapors of said zinc and cadmium sulphides and activator to form a coating of the condensates on a surface of a plurality of base members, placing two coated surfaces of said base members face to face and closely adjacent to each other, heating said two coated base members and the condensates thereon to a temperature between 400 C. and 650 C. substantially solely in the vapors of said condensates and at atmospheric pressure, and separating said two coated base members from each other to form a support having an outer iilm of activated phosphor material.

JOHN E. RUEDY. FERD E. WILLIAMS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,954,691 De Boer Api'. 10, 1934 2,151,457 Williams Mar. 2l, 1939 2,238,026 Moore Apr. 8, 1941 2,280,939 Weinhart Apr. 28, 1942 FOREIGN PATENTS Number Country Date 526,320 Great Britain-...nm Sept. 16, 194:0 

1. THE METHOD OF MAKING A PHOSPHOR SCREEN ON A PLURALITY OF SUPPORTS FROM A PHOSPHOR COMPOUND FORMED OF A METAL FROM THE GROUP CONSISTING OF ZINC AND CADMIUM AND MIXTURES THEREOF AND OF A NON-METAL FROM THE GROUP CONSISTING OF SULFUR AND SELENIUM AND MIXTURES THEREOF, SAID METHOD COMPRISING THE STEPS OF, ARRANGING SAID COMPOUND ADJACENT SAID SUPPORTS WITHIN A VACUUM, VAPORIZING SAID COMPOUND, CONDENSING THE VAPORS OF SAID COMPOUND TO FORM A COATING OF THE CONDENSATE ON A SURFACE OF SAID BASE MEMBERS, PLACING TWO COATED SURFACES OF SAID BASE MEMBER 